Luminescent materials are often used to detect faults, such as leaks. For example, a fluorescent dye is injected or poured into a system. Where a leak occurs the dye will escape from the system. Shining a light of appropriate wavelength (typically ultraviolet) on the system will cause the dye to fluoresce. The existence and location of a leak or leaks are then evident. When performed in total darkness the outcome of such a procedure is often enhanced; however, total darkness is often not available in testing environments, such as an outdoor air conditioner where the sun cannot be shut off, or a shop floor where darkness may be dangerous when machinery in motion is involved.
Unfortunately, visible (including ambient) light competes with the fluorescence from dye for the attention of the person conducting the test. This is particularly true where the system has shiny surfaces that reflect visible or ambient light.
Similarly, luminescent materials are also used in non-destuctive testing. For example, fluorescent dyes combined with iron filings can be used to detect faults such as stress fractures. The combination of iron filings and fluorescent dye is attracted to the faults and, again, the dye emits visible light when illuminated by appropriate incident wavelength light. Even though non-destructive testing may be stringently regulated, the emitted light from a very small fault is often difficult to detect even though a very small fault may present a potentially great danger. Any assistance in identifying these faults would be helpful.
Other concerns with existing ultraviolet lamps are their cost, size and power consumption. For low power consumption and cost, fluorescent lamps can be used to generate the incident radiation. However, fluorescent lamps generate a low intensity of incident ultraviolet radiation. It is desirable to be able to bring the lamp in to close proimity with the fault. This is often difficult in the tight spaces available when working around machinery and equipment.
It is an object of the invention to address these or other problems associated with the use of lamps in the location of faults in machinery and equipment.
As described above in lamps for use in leak-detection and NDT are known. The basic method behind NDT and leak detection is simple. A fluorescent material is applied to a body to be tested in such a way as to highlight a fault in the body when the material is illuminated by shining a lamp emitting ultraviolet light of a particular wavelength on the body.
The fluorescent material can be applied to the body in many ways. The two most common are magnetic particles and liquid penetrants. Magnetic particles are mixed with fluorescent materials and applied to the body. The particles and fluorescent materials form distinctive patterns depending upon the characteristics of the body; for example, metal in aircraft components will act differently in the presence of magnetic fields and thus cause distinctive patterns of magnetic particles applied to the components, depending upon the existence of faults within the components. Such faults are typically caused by previous stresses. Liquid penetrants are also mixed with fluorescent materials to reveal faults by penetrating cracks in a body.
Stringent requirements for NDT lamps are specified in different standards, for example NDT using magnetic particles is covered in American Society for Testing and Materials ("ASTM") Standard Practice for Magnetic Particle Examination designation E 1444 and NDT using liquid penetrant is covered in ASTM Standard Practice for Liquid Penetrant Examination designation E 1417. Leak detection lamps are not typically covered in standards; but, typically benefit from properties required for NDT.
Designation E 1444 specifies the following for magnetic particle testing:
5.7 Lighting:
5.7.1 Visible Light--Visible light shall be used when examining with non-fluorescent particles. The intensity of the visible light at the surface of the part undergoing examination shall be maintained at a minimum of 100 fc (1000 1x). The intensity measurement shall be conducted with a suitable illuminance meter with a photopic spectral response.
5.7.1.1 Ambient Visible Light--Unless otherwise specified, fluorescent magnetic particle examinations shall be performed in a darkened area with a maximum ambient visible light level of 2 fc (20 1x) measured at the part surface.
5.7.1.2 Special Visible Internal Light Source--When examinations of internal surfaces must be performed using special visible light sources, the image produced must have sufficient resolution to effectively evaluate the required discontinuities. Light intensity shall be measured at the expected working distance of the equipment.
5.7.2 Black Lights--All black lights shall be checked at the intervals specified in Table 1, and after bulb replacement, for output. A longer period may be used if a plan justifying this extension is prepared by the nondestructive testing facility and approved by the contracting agency. The minimum acceptable intensity is 1000 uW/cm.sup.2 at the part being examined. Black light reflectors and filters shall be checked daily for cleanliness and integrity. Damaged or dirty reflectors or filters shall be replaced or otherwise corrected as appropriate.
5.7.3 Internal Part Examination--Where lamps are physically too large to directly illuminate the examination surface, special lighting shall be used. Internal features such as bores, holes, and passages less than 0.5 in. (12.5 mm) nominal diameter shall not require magnetic particle examination unless otherwise specified by the contracting agency.
Designation E 1417 specifies similar lighting requirements.
In order to meet the low ambient light requirement and the high black light (ultraviolet A) requirement, a mercury vapour bulb is used with a coloured filter. The combination emits limited visible light and sufficient ultraviolet light.
While they produce relatively high amounts of ultraviolet light, mercury vapour bulbs are quite large and slow to turn on. Halogen bulbs have been used for leak detection with mixed results. Halogen bulbs turns on instantly; however, the bulbs produce limited amounts of ultraviolet light. Halogen bulbs are rarely used for NDT, if at all.